Episode 1: Properties and laws of volatile anesthetics

This is a very high yield episode to help you review for the anesthesia board exam.  I cover the board key word section entitled gas laws which includes a focus on volatile anesthetics, their properties, and how they act on, and in, the human body.

Topics covered will include:

Full post for episode links

Vapor Pressure

Which inhaled anesthetic gas has the highest vapor pressure?
A: Sevoflurane
B: Desflurane
C: Nitrous oxide
D: Halothane
Discussion (3:31)

What is VP proportional to?
Discussion (5:09)

Anesthetic concentration

Vaporizer Types and safety features

If you accidentally filled your sevo vaporizer with iso, what would happen? Why?
Discussion (5:31)

Why does desflurane have its own special type of vaporizer?
Discussion (10:53)

What happens when you use a variable bypass vaporizer at altitude?
Discussion (14:11)

Why would Des be different at altitude?
Discussion (15:15)

Uptake and elimination

Most important concept?
Discussion (15:59)


What effect does a R→L intracardiac shunt have on the rate of inhaled induction of anesthesia?
Discussion (18:50)

Why more effect on poorly soluble agents?
Discussion (19:11)

Additional intracardiac shunt effects (19:50)

What is the blood-gas solubility coefficient?
Discussion (20:33)

Effects of ventilation and circulation

What effect does increased alveolar ventilation have on inhaled induction?
Discussion (22:00)

More affect on soluble or insoluble?
Discussion (22:25)

How is solubility of gas affected by endobronchial intubation?
Discussion (23:53)

How does cardiac output affect onset of inhaled induction?
Discussion (26:16)

Why inhaled induction so fast in infants?
Discussion (27:27)

Second gas effect

What is it? (28:49)

Nitrous Oxide in closed spaces

Common examples (29:35)

Leave questions or comments here or email accracpodcast@gmail.com  

Corresponding ppt slides: Gas_Laws  

Supplemental explanation of some of these topics by Andrew Hershey: Partial pressure analogy

See other interactive posts

13 Replies to “Episode 1: Properties and laws of volatile anesthetics”

  1. This is a great podcast that helps solidify my learning and generate critical thinking. I’m a SRNA and often find myself referring my classmates to this podcast. I just wish there were more! Thank you!

  2. Just stumbled upon your podcast on my commute and wanted to say thank you. It’s great to listen to the discussions while on the road. I just wanted to suggest a correction. My understanding, and I referenced Miller’s Anesthesia to be sure, but Desflurane uses a Tec 6 vaporizer and not a Tec 9 as mentioned in your podcast. My class actually came up with an analogy to help remember this little fact. We call Desflurane the Duke Blue Devil. Blue because of the color coding for Des. Devil because everything involving him surrounds the satanic number 6. For example, MAC = 6%. VP = 666 mmHg, B:G ratio = 0.42 (4+2 = 6), O:G ratio = 18 (3 x 6) and it’s enclosed in a Tec 6 vaporizer.

    1. Hi Patrick, you’re absolutely right. I don’t know where I got tech 9 from but thanks for pointing out the correction!

      Best,
      Jed

  3. I wanted to take a moment to sincerely thank you for all the effort you put into ACCRAC. You are a wonderful teacher & I’ve found ACCRAC to be invaluable. Thank you.

  4. Hi Jed, just wondering if you could clarify – in this talk you talk about volatile anaesthetics in infants, and mention that they have a lower FRC. My understanding is that soon after birth their FRC comes to near adult values at 30 mL/kg.

    Do you mean a lower absolute value for FRC?

    Either way the higher minute ventilation, with larger RR would explain the increased speed of induction.

    Thanks!

    1. Hi Mike,

      Thanks for the comment. I’ve found some conflicting reports about exactly when the FRC on a ml/kg basis comes up to adult values. I think the most important thing is that their minute ventilation to FRC ratio is much greater than an adult’s and that leads to faster induction.

      Best,
      Jed

  5. Hi Jed!

    Thank you so much for your pod cast. Im a dental anesthesia resident, and have found it impossible to learn the material with out guidance. My program doesnt offer any lectures nor structure to the didactic portion of the porgram. Do you by any chance have any porwerpoints, notes, book suggestions, to use in addition to you pod casts. Do you have anything more available than listed on the site? Any help or response would be greatly appreciated. Thank you very much!

    Simone

    1. Hi Simone,

      I’m glad you are enjoying the podcast. In terms of other resources there are the basic textbooks like Baby Miller (the basic version of Miller’s Anesthesia). University of Kentucky has some great YouTube lectures available by searching YouTube for University of Kentucky anesthesia. I hope that’s helpful. Good luck with your ongoing training!

      Best,
      Jed

  6. Dear Jed, I am an anaesthetist in India with about 15 years of experience. While searching for a BJA podcast I stumbled upon yours. I must say this was a fortuitous discovery. I listen to your podcasts while commuting to work in the morning and they set the mood for the day. Have you come across any literature for anaesthetic considerations for surgeries of long duration?

    Keep up the good work! And thank you.

    Sincerely,
    Bhavana

    1. Hi Bhavana,

      I’m so glad you found the podcast and are finding it useful. You ask a great question. I’m not aware of any studies on that specifically. I think in general you would want to be very careful with any agents with long context sensitive half-lives, at least if you were planning on waking the patient up and extubating at the end of the case. For long cases, especially with obese patients, we may use sevoflurane or desflurane instead of isoflurane, or if we use isoflurane we would turn it down early. We might use remifentanil instead of fentanyl as well. If we use a propofol drip we would be very conscious of turning down the dose as the hours go on. Let us know if you have any other thoughts or if you come across any literature on the subject. Thanks!

      Best,
      Jed

  7. Hey Jed,
    I just wanted to thank you for doing these podcasts. I did catch one little error in this one though. I know this one more than a couple years old at this point, but when you are speaking of N2O you stated that it is highly soluble. As far as I understand, N2O is not very soluble but highly diffusible. Just wanted to make sure any new-comers such as myself didn’t get the wrong idea. Thanks again!

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